1. Field of the Invention
The present invention pertains to a process for preparing a foamed polymer, by reacting glycerol with a tri-carboxylic acid.
2. Description of Related Art
Polymer foams are known in the art for various applications, e.g., as packaging material and as insulation material.
A disadvantage of polymer foams known in the art is that they are often based on petroleum-derived sources, which means that they are not renewable, and cannot be classified as “green”. A further disadvantage is that they are not biodegradable, which is of particular importance for packaging materials. A still further disadvantage is that some of the materials comprise heteroatoms or aromatic rings, which may cause issues when the material is combusted, such as the formation of SOx/NOx compounds and the release of toxic fumes.
There is therefore need for a polymer foam which solves these problems.
WO2010/059925 describes a polymer obtained by reaction of glycerol with citric acid in a two-step process. In a first step, low-molecular weight polyester pre-polymers are synthesized at a temperature of 80° C. to 250° C., which are then reacted further at a pressure at or above 1 atmosphere and a temperature of 175° C. to 400° C.
It has been found, however, that the process as described in this document has a number of disadvantages.
It was found that the resulting polymer has an unattractive appearance; it suffers from yellowing and an irregular structure.
Further, the stability of the polymer is insufficient. Analysis of the product obtained by this process shows that the carbon content of the product evidences that degradation of the product takes place. The fact that at temperatures of 150° C. and above some of the citric acid decarboxylates to itaconic acid means that it is no longer possible to obtain a fully cross-linked polymer structure. This causes the changes in the polymer properties. Moreover, because this is an extrinsic factor (i.e., its magnitude is related to the size of the system) the changes and problems as a result of polymerization at 150° C. or above will get worse when the process is carried out on a large scale.